Introduce "hcall" pointer to indicate pending hypercall.

Currently we look at the "trapnum" to see if the Guest wants a
hypercall.  But once the hypercall is done we have to reset trapnum to
a bogus value, otherwise if we exit to userspace and return, we'd run
the same hypercall twice (that was a nasty bug to find!).

This has two main effects:

1) When Jes's patch changes the hypercall args to be a generic "struct
   hcall_args" we simply change the type of "lg->hcall".  It's set by
   arch code, so if it has to copy args or something it can do so, and
   point "hcall" into lg->arch somewhere.

2) Async hypercalls only get run when an actual hypercall is pending.
   This simplfies the code a little and is a more logical semantic.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

diff --git a/drivers/lguest/core.c b/drivers/lguest/core.c
index 06869a2..02556ba 100644 (file)
--- a/drivers/lguest/core.c
+++ b/drivers/lguest/core.c
@@ -198,10 +198,10 @@ int run_guest(struct lguest *lg, unsigned long __user *user)
 {
        /* We stop running once the Guest is dead. */
        while (!lg->dead) {
-               /* First we run any hypercalls the Guest wants done: either in
-                * the hypercall ring in "struct lguest_data", or directly by
-                * using int 31 (LGUEST_TRAP_ENTRY). */
-               do_hypercalls(lg);
+               /* First we run any hypercalls the Guest wants done. */
+               if (lg->hcall)
+                       do_hypercalls(lg);
+
                /* It's possible the Guest did a SEND_DMA hypercall to the
                 * Launcher, in which case we return from the read() now. */
                if (lg->dma_is_pending) {

diff --git a/drivers/lguest/hypercalls.c b/drivers/lguest/hypercalls.c
index 8bde209..0175a9f 100644 (file)
--- a/drivers/lguest/hypercalls.c
+++ b/drivers/lguest/hypercalls.c
@@ -241,19 +241,6 @@ static void initialize(struct lguest *lg)
  * is one other way we can do things for the Guest, as we see in
  * emulate_insn(). */
 
-/*H:110 Tricky point: we mark the hypercall as "done" once we've done it.
- * Normally we don't need to do this: the Guest will run again and update the
- * trap number before we come back around the run_guest() loop to
- * do_hypercalls().
- *
- * However, if we are signalled or the Guest sends DMA to the Launcher, that
- * loop will exit without running the Guest.  When it comes back it would try
- * to re-run the hypercall. */
-static void clear_hcall(struct lguest *lg)
-{
-       lg->regs->trapnum = 255;
-}
-
 /*H:100
  * Hypercalls
  *
@@ -262,16 +249,12 @@ static void clear_hcall(struct lguest *lg)
  */
 void do_hypercalls(struct lguest *lg)
 {
-       /* Not initialized yet? */
+       /* Not initialized yet?  This hypercall must do it. */
        if (unlikely(!lg->lguest_data)) {
-               /* Did the Guest make a hypercall?  We might have come back for
-                * some other reason (an interrupt, a different trap). */
-               if (lg->regs->trapnum == LGUEST_TRAP_ENTRY) {
-                       /* Set up the "struct lguest_data" */
-                       initialize(lg);
-                       /* The hypercall is done. */
-                       clear_hcall(lg);
-               }
+               /* Set up the "struct lguest_data" */
+               initialize(lg);
+               /* Hcall is done. */
+               lg->hcall = NULL;
                return;
        }
 
@@ -281,12 +264,21 @@ void do_hypercalls(struct lguest *lg)
        do_async_hcalls(lg);
 
        /* If we stopped reading the hypercall ring because the Guest did a
-        * SEND_DMA to the Launcher, we want to return now.  Otherwise if the
-        * Guest asked us to do a hypercall, we do it. */
-       if (!lg->dma_is_pending && lg->regs->trapnum == LGUEST_TRAP_ENTRY) {
-               do_hcall(lg, lg->regs);
-               /* The hypercall is done. */
-               clear_hcall(lg);
+        * SEND_DMA to the Launcher, we want to return now.  Otherwise we do
+        * the hypercall. */
+       if (!lg->dma_is_pending) {
+               do_hcall(lg, lg->hcall);
+               /* Tricky point: we reset the hcall pointer to mark the
+                * hypercall as "done".  We use the hcall pointer rather than
+                * the trap number to indicate a hypercall is pending.
+                * Normally it doesn't matter: the Guest will run again and
+                * update the trap number before we come back here.
+                *
+                * However, if we are signalled or the Guest sends DMA to the
+                * Launcher, the run_guest() loop will exit without running the
+                * Guest.  When it comes back it would try to re-run the
+                * hypercall. */
+               lg->hcall = NULL;
        }
 }
 

diff --git a/drivers/lguest/lg.h b/drivers/lguest/lg.h
index 203d310..662994b 100644 (file)
--- a/drivers/lguest/lg.h
+++ b/drivers/lguest/lg.h
@@ -106,6 +106,9 @@ struct lguest
        u32 esp1;
        u8 ss1;
 
+       /* If a hypercall was asked for, this points to the arguments. */
+       struct lguest_regs *hcall;
+
        /* Do we need to stop what we're doing and return to userspace? */
        int break_out;
        wait_queue_head_t break_wq;

diff --git a/drivers/lguest/x86/core.c b/drivers/lguest/x86/core.c
index e2f46b1..0cc251c 100644 (file)
--- a/drivers/lguest/x86/core.c
+++ b/drivers/lguest/x86/core.c
@@ -316,13 +316,14 @@ void lguest_arch_handle_trap(struct lguest *lg)
                        return;
                break;
        case 32 ... 255:
-               /* These values mean a real interrupt occurred, in
-                * which case the Host handler has already been run.
-                * We just do a friendly check if another process
-                * should now be run, then fall through to loop
-                * around: */
+               /* These values mean a real interrupt occurred, in which case
+                * the Host handler has already been run.  We just do a
+                * friendly check if another process should now be run, then
+                * return to run the Guest again */
                cond_resched();
-       case LGUEST_TRAP_ENTRY: /* Handled before re-entering Guest */
+               return;
+       case LGUEST_TRAP_ENTRY:
+               lg->hcall = lg->regs;
                return;
        }